This work presents a study on the thin films of WO3 deposited on a flexible substrate as a possible application in a flexible electrochromic device. The films were prepared by the sol-gel method and deposited by a dip-coating technique on indium fin oxide/poly(ethylene terephthalate) (ITO/PET) and densified at 100 degrees C for 1 h. The films of WO3 were subjected to electrochemical, optical, structural, and morphological characterizations that pointed out the film, deposited with a withdrawal of 60 mm min(-1), which showed the charge density in the insertion process of 32.86 mC cm(-2). This film also presented the electrochemical stability during 200 cycles. The transmittance variation (Delta T-555( )nm) between colored and bleached states was 42.6% and the coloration efficiency (eta) was 14.91 cm(2) C-1. The X-ray diffraction (XRD) confirmed the amorphous structure of the films and the atomic force microscopy (AFM) the root mean-squared (RMS) roughness of 4.15 nm. All the results indicate that this film may be used as an active layer in a flexible electrochromic device.